1. Field of the Invention
This invention relates to a seat assembly, and more particularly, a cushion in a seat assembly for a vehicle.
2. Description of the Prior Art
A seat cushion usually has a depressed central portion which enables a person seated thereon to maintain a stable posture and a nice sitting comfort. A seat cushion essentially comprises a pad formed from a urethane foam, and a cover enclosing the pad. Various methods have been proposed for attaching the cover to the cushion pad in such a way that the cushion may have a depressed central portion.
A conventional seat cushion is generally shown as A in FIG. 1, and has a depressed central portion B. It comprises a cover 1 having a plurality of hanger bags 1a, and a pad 2 in which a wire 3 is embedded. The hanger bags 1a are joined to the wire 3 by a plurality of clasps 4. The reaction of the wire and the clasps against the weight of a person seated on the cushion, however, is generally uncomfortable. Moreover, this seat cushion requires a lot of time to manufacture, and is, therefore, expensive.
Another seat cushion has been proposed to improve the drawbacks of the prior art. It comprises a cover 5 formed from a material which is weldable by high frequency electric heating, a layer of urethane wadding 6, a urethane foam pad 7, and a calico backing 8, as shown in FIG. 4. This seat cushion is manufactured by placing the various members of the cushion between the upper and lower halves 9 and 9' of a high frequency electric welder, compressing them as shown in FIG. 3, and applying a high frequency voltage to the welder to weld the cover 5 and the pad 7 to each other as shown at 5a to 5c in FIG. 4. This seat cushion is, however, unsatisfactory in durability. The joints 5a to 5c are not sufficiently strong and lose their resistance to vibration, friction, or the like, resulting in the separation of the pad from the cover, after a relatively short period of time.